Temperature compensator for a pressure gauge

ABSTRACT

A temperature compensator for a pressure gauge or the like, including a body having a first and second cylindrical cavity coaxial of each other and communicating with each other, a sensing port communicating with one end of the first cylindrical cavity, a vent port communicating with the other end of the first cylindrical cavity, and a compensating port communicating with the second cylindrical cavity, a sense responsive piston positioned in the first cavity intermediate the sensing and vent ports, a compensating piston positioned in the second cavity, the sense responsive and compensating pistons being affixed to each other for simultaneous axial movement, resilient means urging the sense responsive piston towards the sensing port and thereby the compensating piston towards the compensating port, and a closed temperature sensing vessel having communication with the sensing port.

United States Patent 1 June 20, 1972 Primary Examiner-Donald O. WoodielAttorney-Head & Johnson [57] ABSTRACT A temperature compensator for apressure gauge or the like, including a body having a first and secondcylindrical cavity coaxial of each other and communicating with eachother, a sensing port communicating with one end of the firstcylindrical cavity, a vent port communicating with the other end of thefirst cylindrical cavity, and a compensating port communicating with thesecond cylindrical cavity, a sense responsive piston positioned in thefirst cavity intermediate the sensing and vent ports, a compensatingpiston positioned in the second cavity, the sense responsive andcompensating pistons being affixed to each other for simultaneous axialmovement, resilient means urging the sense responsive piston towards thesensing port and thereby the compensating piston towards thecompensating port, and a closed temperature sensing vessel havingcommunication with the sensing port.

5Clalms, 3Drawingl1gures Corry [54] TEMPERATURE COMPENSATOR FOR APRESSURE GAUGE [72] Inventor: Stuart E. Corry, 451 l S. Lewis Place,Tulsa, Okla. 74105 [22] Filed: Dec. 23, 1970 [2|] Appl. No.: 100,880

[52] US. Cl. ..73I393,73I368.3, l77/209 [51] Int. Cl. ..G0ll 19/04 [58]Field of Search ..73/393, 368.3, 368.8, 419; 92/1, 5 R; 177/208, 209

[56] References Cited UNITED STATES PATENTS 2,324,217 7/1943 Knauth..73I393 /2 I r i 13* 1 LL: r i fril'f'l, 9 I65 5: 16A J .--/8B k.- n 1p 1 1311 I PATENHnJmo m2 SHEET 1 UF 2 ATTORNEYS PATENTEDJum I972 3, 670,576

sum 2 or 2 STUART E. CORRY 404 j A r TOR/V5 rs TEMPERATURE COMPENSATORFOR A PRESSURE GAUGE BACKGROUND, SUMMARY AND OBJECTS OF THE INVENTIONHydraulic or pneumatic load cells are frequently used for weight andforce measurements in industry. In a simple application only a singleload cell may be required but in many industrial applications more thanone load cell is needed. To weigh a vessel and its contents it issometimes necessary to employ two, three, or four load cells dependingupon the size and method of support of the vessel. When the load cellsare used to weigh trucks, four, six, or even eight load cells may berequired, one being positioned under each wheel or set of wheels of thetruck, to ascertain the total vehicle weight.

In order that weight or force measurements detected by a plurality ofload cells can provide a single indication of the total weight of forcebeing measured, the use of pressure totalizers or pressure integratorsis employed. For more information about such pressure totalizersreference may be had to U.S. Pat. No. 3,l98,0l4, issued Aug. 3, I965,Stuart E. Corry, inventor, and entitled Pressure Integrator." Pressureintegrators utilize a piston which is moved in the integrator to forcefluid to a pressure indicating gauge. The piston is moved by thesummation of a plurality of pressures and thereby the pressure appliedby the integrator to the single gauge is indicative of a summation orintegration of a plurality of weights or forces. The use of pressureintegrators is completely satisfactory for many applications. Oneproblem, however, which is sometimes encountered, is that of fluctuationof gauge readings due to temperature changes. The hydraulic fluidnormally employed in the line between the pressure integrator and thetotalizing gauge represents a fixed and confined volume. When theintegrator piston moves so that the fluid volume is shifted towards oraway from the gauge, the gauge reflects such movement, but regardless ofthe position of the piston the volume of fluid contained in the interiorof the integrator summarization piston and in the line between theintegrator and the gauge remains fixed. If the temperature of this fluidincreases, the movement of the fluid is, at least partially, toward thegauge which causes the gauge to reflect a higher reading.correspondingly, if the temperature of this fixed volume of fluiddecreases, the gauge reflects a decreased rating. This inventionprovides a device for overcoming the problems of the above described.

It is therefore a primary and basic object of the invention to provide atemperature compensator for a pressure gauge or the like.

A more particular object of this invention is to provide a device whichmay be affixed to a pressure indicating gauge for automaticallycompensating for temperature changes whereby the gauge accuratelyreflects pressure applied to it irrespective of temperature changes.

A still more particular object of this invention is to provide atemperature compensator for inserting in communication with the linebetween a pressure integrator and pressure gauge so that the pressuregauge is thereby unaffected by temperature changes.

These and more particular objects of the invention will be fulfilled byapparatus described in the following specification and claims, taken onconjunction with the attached drawings.

DESCRIPTION OF THE VIEWS FIG. I is a diagrammatic representation of atemperature compensator, shown in cross section, as applied to apressure integrator and pressure gauge for indicating the weight of avessel, the temperature compensator serving to compensate for changes intemperature in the hydraulic fluid between the integrator and the gauge.

FIG. 2 is an end view of an embodiment of the temperature compensator ofthis invention.

FIG. 3 is a cross-sectional view taken along the line 33 of FIG. 2.

DETAILED oescmrnou Referring to FIG. 1, a temperature compensator isshown in crossFsectional view and generally indicated by the numeral 10.The temperature compensator 10 will be described as it is utilized as apart of a system for indicating the weight of a vessel 12 by means of agauge 14. Vessel l2 rests on load cells 16A and 168, each of whichapplies hydraulic pressure by way of lines 18A and 188 respectively, toa pressure integrator or totalizer 20. As previously mentioned, U. S.Pat. No. 3,198,014 describes in detail a pressure integrator of the typeexemplified by the numeral 20. The output of integrator 20 at line 22 isa pressure representative of the total applied by the two load cells 16.The volume of fluid in line 22, in gauge l4, and in the totalizingcylinder of integrator 20 remains fixed. When a temperature changeoccurs in this fixed fluid volume, the reading of gauge 14 will change.Since gauge 14 is utilized to indicate the total weight of vessel 12 andthereby to indicate the change in the quantity of contents of thevessel, a change in temperature would thereby cause an erroneous readingas to the quantity of contents of the vessel. The function of thetemperature compensator 10 of this invention is to compen sate fortemperature change so that gauge 14 accurately reflects the pressureoutlet from integrator 20 regardless of temperature change.

The integrator 10 includes a body 26 having a first closed end 26A and asecond closed end 268. Within the body is a first cylindrical cavity 28and, coaxially with it, a second cylindrical cavity 30. The cavity 30communicates with the first cavity 28. Slidably positioned within thefirst cavity 28 is a sense responsive piston 32 which may include anO-ring 34 to insure that no leakage occurs past the piston. In a similarmanner, positioned within the second cylindrical cavity 30 is acompensating piston 36 which is also shown as having an O- ring 38.Pistons 30 and 32 are coaxial of each other and are affixed to eachother for simultaneous axial movement within body 26.

Communicating with first cylindrical cavity 28 adjacent body first end26A is a sensing port 40. in addition, communicating with the firstcylindrical cavity 28 at body end 268 is a vent port 42. Communicatingwith the second cylindrical cavity 30 is a compensating port 44.

Afiixed to and extending coaxially from sense responsive piston 32 is aspring guide 46. Filled about guide 46 is a compressed coiled spring 48which extends between piston 32 and body end 268 to resiliently urgepiston 32 in the direction towards sensing port 40. End 268 is shown asbeing removable and held to the body 26 by means of bolts 50. Affixed tothe outer end of spring guide 46 is a coaxial rod 52 which serves togive visual indication of the position of pistons 32 and 36 in thecompensator.

Communicating with sensing ports 40 is a closed temperature sensingvessel generally indicated by the numeral 54. In the illustratedarrangement the vessel 54 is in the form of a tube closed at its outerend 54A and having the inner end suitably engaging the sensing port 40,such as by means of a compression fitting 56.

While the temperature compensator functions either on the hydraulic orpneumatic systems, the most common application is with hydraulicsystems. When used with a hydraulic system the interior of cylinder 28between sensing port 40 and piston 32 is filled with hydraulic fluid,and the temperature sensing vessel 54 is filled with such fluid. Cavity30 is filled with hydraulic fluid. Port 44 receives a line 58 whichextends to the line 22 so that the pressure of fluid in line 22, andthereby in gauge 14, is the same as that in second cylindrical cavity30.

OPERATION OF EMBODIMENT OF FIGURE 1 Compensator 10 functions fortemperature changes on the system load cells 16A and 16B and integrator20 by a volume balance design placed on the output of the integratorswith the same pressure imposed on it as is on the read out gauge 14. Thefunction of compensator 10 is such that the pressure on piston 36balances against spring 48 on the vented side of the piston 32. Fluid isfilled in the cylinder 26 through the temperature sensing tube 54, andis filled at the time maximum pressure is on the spring 48 by the forceof the integrator on piston 36 and when the temperature of both systemsare the same. An additional pressure is put in cylinder 28 to compressthe spring 48 an additional small amount. The compensator system is nowready to operate.

As the temperature decreases the contraction of the fluid in temperaturesensing vessel 54 and cylinder 28 allows the force in spring 48 to movethe piston 36 into the cylinder 30 replacing the loss of fluid volumecaused by the temperature drop in the load cell and in line 22. As thetemperature increases, the increase in volume of fluid in cylinder 28and temperature sensing vessel 54 compresses the spring 48, moving thepiston 36 out of the cylinder 30 reducing the pressure that has beenincreased by the rise in temperature in the load cell and integratorsystem.

ALTERNATE EMBODIMENT FIGS. 2 and 3 show an alternate embodiment of thepressure integrator. The embodiments of FIGS. 2 and 3 function exactlythe same as described with reference to FIG. 1 but illustrate a moresophisticated design, more representative of a typical commercialproduct embodying the invention. A plate 60 is affixed to the senseresponsive piston 32. Extending from plate 60 are a plurality of springguides, there being five such guides illustrated identified by thenumerals 46A through 46E.

Each of the spring guides 46A through 4615 is parallel to the axis ofpiston 32 and guide 46B is coaxial with piston 32. Each of the guidesreceive a coiled compression spring, being designated 48A through 4815.Rod 52 extends from the spring guide 468.

The body end 26B in the embodiment of FIGS. 2 and 3 includes recesses62, there being one recess for each of the spring guides. Bolts 64extend from the body end 26B to the opposed body end 26A as a means ofassembly of the components of the body together. Plate 60 has notches 66to receive bolts 64 so that piston 32 moves freely in response tohydraulic pressure. Instead of notches 66, plate 60 may be provided withopenings to receive bolts 64.

Two sensing ports 40A and 40B are shown for convenience in makingconnection to the temperature sensing system. One or the other of thesensing ports 40A and 408 will normally be closed by a plug. Theembodiment of FIGS. 2 and 3 functions exactly the same as described withreference to the embodiment of FIG. I.

It can be seen that the essence of the invention is the concept ofremoving fluid from a closed indicating system in which the volume ofthe fluid has been increased by temperature by a compensator actuated bythe same temperature increase.

While the invention has been described with a certain degree ofparticularity it is manifest that many changes may be made in thedetails of construction and the arrangement of components withoutdeparting from the spirit and scope of this disclosure. lt is understoodthat the invention is not limited to the embodiments set forth hereinfor purposes of exemplification but is limited only by the scope of theattached claim or claims, including the full range of equivalency towhich each element thereof is entitled.

What is claimed:

1. A temperature compensator for a pressure gauge or the likecomprising:

a body having a first cylindrical cavity and a second cylindrical cavitycoaxial with and communicating with the first, a sensing portcommunicating with one end of the first cylindrical cavity and a ventport communicating with the other end of the first cylindrical cavity,and a compensating port communicating with the second cylindricalcavity;

a sense responsive piston positioned in said first cavity intermediatesaid sensing and vent ports;

a compensating piston positioned in said second cavity said senseresponsive and compensating pistons being affixed to each other forsimultaneous axial movement;

resilient means urging said sense responsive piston towards each sensingport and thereby said compensating piston towards said compensatingport; and

a closed temperature sensing vessel having communication with saidsensing port.

2. A temperature compensator according to claim I wherein saidtemperature sensing vessel is in the form of a tube having one endclosed and the other communicating with said sensing port.

3. A temperature compensator according to claim I wherein said firstcylinder cavity between said sensing port and said sense responsivepiston, and said temperature sensing vessel, are filled with a heatexpanding liquid.

4. A temperature compensator according to claim I wherein said ventopening in said body is coaxial with said cylindrical cavities andincluding:

an indicating rod affixed coaxially to said sense responsive piston andcoaxially received in said vent opening and extending partiallyexteriorly of said body.

5. A temperature compensator for a pressure gauge according to claim 1including:

a plurality of spring guide members affixed to and extending from andparallel the axis of said sense responsive piston in the directionopposite said sense port, and wherein said resilient means includes aspring compressibly received about each of said spring guides and urgingsaid sense responsive piston towards said sense port.

1. A temperature compensator for a pressure gauge or the likecomprising: a body having a first cylindrical cavity and a secondcylindrical cavity coaxial with and communicating with the first, asensing port communicating with one end of the first cylindrical cavityand a vent port communicating with the other end of the firstcylindrical cavity, and a compensating port communicating with thesecond cylindrical cavity; a sense responsive piston positioned in saidfirst cavity intermediate said sensing and vent ports; a compensatingpiston positioned in said second cavity, said sense responsive andcompensating pistons being affixed to each other for simultaneous axialmovement; resilient means urging said sense responsive piston towardseach sensing port and thereby said compensating piston towards saidcompensating port; and a closed temperature sensing vessel havingcommunication with said sensing port.
 2. A temperature compensatoraccording to claim 1 wherein said temperature sensing vessel is in theform of a tube having one end closed and the other communicating withsaid sensing port.
 3. A temperature compensator according to claim 1wherein said first cylinder cavity between said sensing port and saidsense responsive piston, and said temperature sensing vessel, are filledwith a heat expanding liquid.
 4. A temperature compensator according toclaim 1 wherein said vent opening in said body is coaxial with saidcylindrical cavities and including: an indicating rod affixed coaxiallyto said sense responsive piston and coaxially received in said ventopening and extending partially exteriorly of said body.
 5. Atemperature compensator for a pressure gauge according to claim 1including: a plurality of spring guide members affixed to and extendingfrom and parallel the axis of said sense responsive piston in thedirection opposite said sense port, and wherein said resilient meansincludes a spring compressibly received about each of said spring guidesand urging said sense responsive piston towards said sense port.